Full disclaimer: I am a Sphinx AC committee member!
I ran it in 2009 whilst still unaffiliated. I had only been running since about August 2009 and had just done Coventry Half Marathon in the October, so I was still a very inexperienced runner when I did the Coombe 8.
I would say that you don't need specialist trainers (certainly not spikes) but the terrain is uneven in places so you will definitely benefit from off-road/trail shoes. There are some short, sharp climbs on mud and grass/foliage, so road shoes definitely won't cut it.
As for gym work, the main difference between plain road running and an event like this (to me, anyway) is the amount of side-to-side load placed on your legs and ankles.
If you enjoy running then I think you'll love the Coombe 8. It was the thing that convinced me to join Sphinx AC. We are as passionate about putting on a great event for you as you are at putting in a good performance.
Your entry fee covers your entry to the race but you also get free car parking, long-sleeved t-shirt, hot soup, water, gorgeous scenery, enthusiastic marshals, professional first-aid/paramedic. Approximately 1 in 10 runners will receive some kind of prize - random/spot prizes will be given out so you don't even need to be a category winner or top-performing athelete to win something.
We're offering an "early-bird" discount of £2 off entries received by 21 October. You can enter online through RW or by downloading our 2012 Sphinx AC Coombe 8 entry form, filling it in and posting it off.
We really, really hope to see you on the day as it's a "must-do" event in the region these days. I'll be there, probably doing computerised entries and results but probably snapping away with my camera too.